Device for reducing the de-ionization time in glow discharge tubes and the like



June 26. 1956 B. WESTBERG 2,752,531

J. DEVICE FOR REDUCING THE DEIONIZATlON TIME IN GLOW DISCHARGE TUBES ANDTHE. LIKE.

Filed Dec. 3, 1952 IIVVE/VTOR DEVICE FOR REDUCING THE DE-IONIZATIONTIlVIE IN GLOW DISCHARGE TUBES AND THE LIKE Johan Bertil Westberg,Stockholm, Sweden, assignor to Telefonaktiebolaget L M Ericsson,Stockholm, Sweden, a Swedish company Application December 3, 1952,Serial No. 323,741

Claims priority, application Sweden December 8, 1951 8 Claims. (Cl.315-335) The present invention relates to devices in glow dischargetubes for the purpose of making these swifter in work and thusincreasing their fitness for use in counters and the like. For thispurpose it is necessary to reduce that time which is needed to enable aglow discharge tube after extinction to regain its whole ignitionvoltage or at least the greater part of the same. This time is calledde-ionization time as it is the ionization condition in the gasatmosphere that determines at which voltage the tube is to be ionizedagain. This is applicable on the assumption that the voltage is lowerthan the static ignition voltage obtained without ionization. Thede-ionization time may be reduced by choosing a suitable gas filling anda suitable pressure and by giving the electrode system an especialshaping.

In gas discharges there generally appear three types of charge carriers,viz. free electrons, positive and negative ions. The last mentioned onesare generated through storing of electrons in neutral gas molecules.After an extinction produced by the voltage being lowered below thesustaining voltage a de-ionization of the gas atmosphere is begun,whereby the charge carriers on one hand diffuse (ambi-polarly) toelectrodes and walls, where they are neutralized, on the other get intodirect collision, whereby neutral molecules are again generated(recombination). The characteristic thing for the first-men tionedprocess is that its velocity decreases with increasing pressure, wherebythe diiiusion constant is reciprocally proportional to the pressure,while the recombination increases strongly with increased concentrationand increased pressure. The diifusion predominates at low pressures, e.g. for pure argon at about 1 mm. Hg and below, whereas the recombinationprevails at higher pressures (10 mm. Hg and upwards in pure argon).

In pure rare gases one more kind of particles must be considered, viz.the metastable atoms. These atoms produce new charge carriers even arather long time after the extinction of the glow discharge, therebyincreasing the deionization time most considerably. All rare gases havemetastable energy levels, and therefore non-rare multiatomic gases mustbe utilized, which lack metastable conditions. Non-rare gases possess alarge number of energy levels and are therefore well adapted asadditional gases to rare gases, whereby the rare gas atoms swiftly losetheir metastable energy to the molecules of the additional gas.

Mixtures of rare gases and non-rare gases have early been used fordifferent purposes. Thus for instance hydrogen gas (alternating withargon and mercury) has been added in small quantities to neon and heliumin dim glowing lamps, due to which a lower ignition voltage has beenobtained (Penning efiect). Nitrogen gas has furthermore been usedtogether with rare gases in incandescent lamps for the purpose ofpreventing glow discharge between the lead-in wires. An account of theseearlier applications is to be found in Espe-Knoll: Werkstoifkunde derHochvakwumtecknik (Verlag von Julius Springer, Berlin 1936), page 234.

tfited States atent The fact of the matter is, broadly speaking, thatnonrare gases tend to increase the striking and sustaining voltage inglow discharge tubes. Electronegative gases as oxygen and halogens areespecially unsuitable, on one hand because they alfect the electrodes,on the, other owing to their great electron afiinity, which causes ahigh ignition voltage. A suitable gas is hydrogen gas which howevershould not be used alone but together with one or more rare gases. Theconcentration is not critical but can be varied from some per cent up to15-20%. The tie-ionization time is thereby reduced most considerably asappears from the table below. A gas mixture of this type has earlierbeen used in glow discharge tubes of triode type and in tubes containinga plurality of cathodes for sequential ignition (see for instance theBritish Patent That de-ionization time, which is obtained with gasfillings containing hydrogen gas, is also very much dependent on thepressure (within the area actual for glow discharge tubes) and decreaseswith increasing pressure. This proves that the recombination is ofcrucial importance in this respect.

A stronger diffusion to the electrodes is obtained, if one or moreelectrodes in the tube are connected to a certain voltage after theextinction. This voltage, which is not sufiicient to enable the tube tobe ionized, is yet sufficiently great to accelerate the diifusioneliectively. This may occur either by making the extinguishing pulse sosmall, that the greater part of the anode voltage is maintained afterthe extinction or still more eliectively by introducing in the tube ascreen grid electrode enclosing the anode as Well as the cathode andbeing connected to a voltage over the cathode which is lower than thesustaining voltage. Such a screen has been used in the triode of theabove-mentioned British patent. The tWo-above-mentioned methods forde-ionization, viz. increase of the pressure and introduction of ascreen grid electrode, are both impaired by certain drawbacks. Thepressure must be great, at least about 70 mm., to be fairly eifectiveand this causes high ignition voltages and current densities, whichsometimes is not desirable at all. The screen grid electrode means agreat drawback from a technical manufacturing point of view, and causesfurthermore that an additional voltage must be supplied to the tube.

The present invention has for a purpose to eliminate the two mentioneddrawbacks and like the device with the above-mentioned screen it makesuse of the de-ionizing capacity of an electric field.

On the annexed drawing there is shown in Fig. 1 an example of a glowdischarge tube according to the invention. In Fig. 2 there is shown apulse connection of a glow triode and in Fig. 3 another pulse connectionof a glow triode.

The tube shown in Fig. 1 is provided with a tube envelope with aconductive coating arranged on the outside. This coating covers whollyor partly the outer surface of the tube envelope. If the coating 1 isconnected to a voltage which is constant in relation to the cathode 2 ofthe tube, the potential of the inner side of the tube envelope will beaffected capacitively, so that it can be maintained high after theextinction instead of decreasing with the potential of the anode 3. Thattime during which the wall potential is maintained high is suificient toreduce the tie-ionization time considerably also in pure rare gas tubes.The greatest effect, however, is obtained in tubes with an addition of anon-rare gas as hydrogen gas to the tube atmosphere. As appears from thetable below the de-ionization time is most reduced at low pressures,viz. three to four times, and the remaining difference between diiierentpressures is rather insignificant.

[Table oyer the de-ionization time (in microseconds) in tubes accordingto Fig. 1 on the drawing. Cathode material Ni. Rectangular extinguishingpulse on the anode] IDs-ionization time Pressure,

Gas mm. Hg

With coating Without coating DID-1H IO p eamp- 0 The advantage of thecoating on the glass envelope is that it may be applied to any potentialwhatever and consequently also to earth potential. Thus the wallpotential of the inner side becomes the right one automatically.

For obtaining the best result the coating should for alternatingcurrents be connected to the cathode in those cases when the potentialof the same is not constant during the extinction. This is. shown inFigs. 2 and 3. Fig. 2 shows an example of a pulse connection of a glowtriode with an earthed cathode 2. The coating 1 is hereby also connectedto earth. 4 indicates an ignition anode, to which ignition pulses aresupplied. In Fig. 3 there is shown an example of a pulse connection of aglow triode with an RC-circuit in the cathode connection wire. Thereference numerals in Fig. 3 correspond to those of Fig. 2.

The coating 1 may also be replaced by a loose screen, but this should inthat case enclose the tube so that the capacity may be maintained.

The device according to the invention is not limited to the embodimentsshown on the drawing but may to advantage be applicable to glowdischarge tubes of the kind described in application Ser. No. 311,966.

I claim:

1. A glow discharge device comprising an envelope containing a gaseousatmosphere composed of rare gas and hydrogen, an anode, and a cathodeand a triggering electrode within said envelope, and an electrodedisposed upon the outside wall of said envelope thereto and at leastpartly covering the envelope, the said outer electrode being connectedto a point having a potential during operation fixed relative to theoperational cathode voltage and coacting capacitatively with theoperational potential on the inner side of the envelope for maintainingsaid latter potential higher than the anode potential decreasing uponextinction of the device whereby the deionization time of the device isreduced;

2. A glow discharge device according to claim 1, wherein the saidoutside electrode is in form of an electrically conductive coatingapplied to the outer wall of said envelope and covering the said wall atleast partly.

3. A glow discharge device according to claim 1, wherein the saidoutside electrode is in form of a screen closely hugging theconfiguration of the outer wall of said envelope.

4. A glow discharge device according to claim 1, wherein said outsideelectrode is connected to a constant potential.

5. A glow discharge device according to claim 1, wherein the saidoutside electrode is connected to the cathode.

6. A glow discharge device according toclaim 1, wherein the saidenvelope contains at least three electrodes.

7. A glow discharge device according to claim 6, wherein the saidenvelope includes electrodes arranged to maintain a continuoussmalldischarge.

8. A glow discharge device comprising an envelope containing a gaseousatmosphere composed of rare gases and hydrogen, an anode, a cathode anda trigger electrode within said envelope, an electrode disposed on theoutside of the envelope at least partly covering the same, said outerelectrode, for alternating current, being directly connected to thecathode.

References Cited in the file of this patent UNITED STATES PATENTS1,517,466 Schaller Dec. 2, 1924 1,889,749 Jobst Dec. 6, 1932 1,965,187Hartman July 3, 1934 2,103,439 Swart Dec. 28, 1937 2,415,816 Depew Feb.18, 1947 2,427,663 Mateosian Sept. 23, 1947 2,445,782 Kruithof July 27,1948 2,487,437 Goldstein Nov. 8, 1949 2,521,315 Victoreen Sept. 5, 19502,525,768 Bruns Oct. 17, 1950 2,633,540 Wilson Mar. 31, 1953 FOREIGNPATENTS 865,357 France Feb. 17, 1941

